Blender Sequencer speed is Extremely slow
Keep UI


render with "Keep UI" option in the Render properties panel under Display
(Just don't let blender display the rendering process in any window.) That was a noticeable speed up for me.


Multicore rendering  


use one of the available scripts for multi-core rendering. Basically a script that opens as many instances of Blender as you have cpu cores or as many as you specify.
(Blender use for VSE render only one core of CPU by default. So even with a two core processor you get only half the render time. If you have an 8core CPU it would be great speed boost for you.)


Parallel Render - Addon, simple to use, but it generates separate movie files - one for each blender instance (that runs on each core separately).
After download, installation, enable ... you run this script with SPACEBAR search, type "parallel ..."

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video_editor_render_script - A python script whit it you need to arrange a few things first, but then it's a ONE-CLICK option with one animation file.
(Namely -download also ffmpeg and specify paths to blender and to ffmpeg in the script. Just follow instructions. In general it also generates separate files for each core first, but than use ffmpeg to merge them in one file.)